When replacing the high/low beam lamp do not touch the lamp bulb with your fingers. Due to the high temperature during operation, any surface contamination (e.g. fingerprints) burns in, leaving dark spots. This leads to local overheating of the glass and can cause the bulb to break.
When installing, hold the lamp by the base only. If the bulb is accidentally touched, it must be thoroughly wiped with a lint-free cloth moistened with alcohol or glass cleaner.